Thermionic discharge device



I Jan. 7, 1936. E. F. .LOWRY THERMIONIC DISCHARGE DEVICE Filed Sept. 18, 1954 INVENTOR Erwin FL awry.

WITNESSES ATT RNEY Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE 'rnianiuromc DISCHARGE DEVICE Erwin F. Lowry, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh,

Pennsylvania Pa., a corporation of Application September 18, 1934, Serial No. 744,505

1 Claim.

An object of my invention is to permit a limited amount of direct radiation from a hot cathode to be directed upon the condensed metallic va- 10; per for starting purposes and yet to protect the condensed metallic vapor from excessive heat radiation during the operation of my device.

In mercury filled thermionic devices, particularly in the larger sizes, it is necessary to bring 15 very rapidly the temperature of the condensed mercury up to a certain temperature in starting so that the tube will take full plate load without excessive arc drop. If an oxide coated cathode is used, then an excessive arc drop is apt to re- 20 sult in injurious bombardment of the oxide coating from the heavy ions of the mercury. On the other hand, it is quite as important to prevent the temperature of the condensed mercury from becoming too high during .the operation of the 25 device because this increased temperature will result in an increased vapor pressure and the excess vapor pressure may deposit particles of mercury on the anode and make a very favorable condition for a backfire. I 30 Accordingly, it is an object of my device to permit very rapid'evaporation of-the condensed mercury in starting so that a suflicient quantity of vapor is available to sustain the are between the anode and the cathode and yet to prevent 35 excessive vapor pressure during the operation of the device so that backfire is also prevented.

Other features and advantages of my invention will appear from the following description, taken in connection with the accompanying draw- 4 ing, in which I Figure 1 is a longitudinal section of an electric discharge device incorporating a preferred form of my invention. v

Fig. 2 is a horizontal cross section taken on 45 lines 11-11 of Fig. 1. b r

In the drawing, the electron discharge device has the container l and this container is preferably provided with a pocket portion II which may conveniently contain the presses I2 50 and I3 for lead-in wires. This pocket II is preferably at one end of the tube and this end is normally the bottom portion when the tube is in operation. At the other end of the tube is preferably located the anode I 4 with its lead 55 wire l5 passing through the glass to. a cap 16 or to othermeans of connecting the anode or plate circuit thereto. Intermediate the anode and the pocket II is the cathode structure l1. While this may be of any construction suitable for a hot cathode, I prefer to make it similar to the 5:

cathode structure disclosed in my copending application, Serial No. 612,505, filed May 20, 1932 for high efficiency oxide coated cathode.

In the drawing, I have somewhat simplified.the

cathode structure disclosed in my copending application to show a coil filament I8 within a casing l9. This coil filament is preferably coated with an oxide coating, namely the barium and strontium oxide familiar to those skilled in this particular art. One end of this filament is connected to the lead-in wire passing through the press l3. The other end of the filament is preferably connected to the casing I9 which is, in turn, connected to the lead-in wire 2| passing through the press I 2. The casing 19 prevents 20 excessive radiation laterally of the cathode and this casing l9 may have one or more walls and a cover 32 with a space for the passage of electrons between it and the casing 19, such as is disclosed in my copending application. The interior of the device, during operation, is intended to be filled with a mercury vapor and this mercury vapor, when condensed, will form a liquid 22 in the bottom of the tube. The quantity of liquid 22 in the bottom of the pocket H will be greater when the tube is not in operation but the amount therein will, of course, decrease as the tube is placed in operation. I

As previously stated, it is desired to create a sufiicient vapor pressure of the mercury immediately upon placing the tube in operation without having an excessive vapor pressure when the tube is operated to cause backfire. In order to start the tube rapidly, I provide an opening 23 of limited area in the bottom portion of the casing or shield l9 about the filament I8. I also place one and preferably more radiation shields 24 and 25 in the bottom of the tube and preferably in the pocket section II, as disclosed in the drawing. These radiation shields 24 and 25 may be of any suitable material such as nickel and may be conveniently supported on one of the leadin wires such as by welding to the wire 2| at the places 26 and 21. These shields 24 and 25 have openings 28 and 29 therein that are aligned with the opening 23 in the casing I 9. The shields 24 and 25 are preferably spaced a slight distance from the walls of the pocket I I so that condensed mercury dropping down to the pocket II will not be deposited thereon.

When the tube is connected for operation, the filament I8 will become hot and a limited portion of the direct heat radiation therefrom will pass through the aligned openings 23, 28 and 29 to fall upon the liquid mercury in the bottom of the pocket I I and vaporize it so that a suflicient mercury vapor pressure will be present within the container to start the are between the cathode I1 and the anode I 4. The shields 24 and 25, however, will prevent excessive heat radiation from vaporizing an excessive portion of the mercury 22 and thus preventing an excessive vapor'pressure within the tube that will cause backfire. The shields prevent heat radiation from the anode and the are or glow around it from affecting the condensed mercury.

The invention is also applicable to tubes in which one or more grids, such as the grid 30, are interposed between the cathode and anode for controlling the operation of the device. This grid 30 may have a connection 3| on the side of the tube, as shown or may have its lead-in wire passing through the pocket I I in a manner similar to the cathode leads 2!! and 2i.

My invention is also particularly adapted for the grid controlled mercury vapor tubes because excessive temperature of the mercury and consequent excessive vapor pressure will change the control characteristics of such a grid-type mercury tuba The condensed mercury is also screened from radiation from these grids.

While I have mentioned mercury as the vet porizable substance, it is to be understood that other substances such as gallium and the various amalgams may also be used.

While I have disclosed the cathode construc- 5 tion of my preferred type, it is apparent that other types of cathode construction than that disclosed at I! may be used. The cathode construction may be merely a filament coil either in the same axial direction, as shown on the drawing, or at right angles thereto. Other obvious changes may be made in the number and shape of the various elements, such as the number of shields.

These various modifications and others may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed upon my claim as are required by the prior art.

I claim as my invention:

An electric discharge device comprising a container, a pocket in one end of said container, a vaporizable metal in said pocket, an anode at the other end of said container, an incandescible cathode intermediate said pocket and said anode, 25 a plurality of shields between said cathode and said pocket and aligned openings in said shields for permitting a limited amount of direct heat radiation from said cathode to said pocket.

80 ERW'IN F. LOWRY. 

